1. Field of the Invention
The present invention relates to scraper blades which are used to remove residual material clinging to the return run of a conveyor belt and, in particular, to primary scraper blades used in pre-cleaner applications located at the head pulley of the conveyor belt. The present invention also relates to processes and methods of designing both primary and secondary scraper blades.
2. Background Art
Scraper blades were previously made such that just the scraping edge of the blade face surface initially engaged the conveyor belt, rather than the entire or full blade face surface, when installed. This edge contact type of blade design cleans with high efficiency when new, but after the blade wears for a short period of time cleaning effectiveness is lost. Scraper blades that provide full-face contact between the face surface of the blade and the conveyor belt, such as those of the present invention, can be designed to maintain constant cleaning efficiency over their wear life. Full-face contact blades extend the life of the blade, particularly on high speed conveyors because a full-face contact blade has more mass to absorb the heat of friction generated with the rotating belt. Full-face blades also eliminate a problem known as feathering which occurs with primary cleaner blades when just the scraping edge engages the belt.
During operation, the scraping edge and the scraping surface of each scraper blade wears due to its scraping engagement with the rotating conveyor belt. The tensioner rotates the cross shaft and the scraper blades to maintain the scraper blades in biased scraping engagement with the conveyor belt. As the scraper blades wear and are rotated into continuing engagement with the conveyor belt, the orientation of the scraper blades with respect to the conveyor belt changes, which typically causes a change in the cleaning angle between the surface of the conveyor belt and the front surface of the scraper blade at the scraping edge, and a change in the scraping pressure with which the scraper blade engages the conveyor belt.
U.S. Pat. No. 4,917,231 is owned by the applicant herein and is incorporated herein by reference and discloses a constant angle conveyor belt cleaner. A scraper blade is disclosed having a curvilinear scraping face and a rear face. A tip face extends between rear face and the scraping face. The tip face and the scraping face meet at a scraping edge. The scraper blade, belt and pulley define a cleaning angle. The cleaning angle is the tangent angle formed between the tangent of the belt at the point of contact by the scraper blade, and the line extending from a distal end of the scraper blade in a direction toward the belt and head pulley. The scraper blade maintains a constant cleaning angle throughout the wear life of the blade. U.S. Pat. No. 6,439,373 is assigned to the instant assignee herein and is incorporated herein by reference and discloses a constant angle and pressure conveyor belt cleaner and tensioning arrangement. A scraper blade is disclosed having a front surface, a rear surface, and a blade face surface. The blade surface is curved to conform to the curvature of the conveyor belt such that the entire blade face surface will engage the belt in full-face contact. The blade provides a curve which defines an involute of a circle.
U.S. Pat. No. 6,457,575 is assigned to the instant assignee herein and is incorporated herein by reference and discloses a self-locking pin mounting arrangement for conveyor belt cleaner scraper blades. U.S. Patent Application Publication Nos. 2006/0108200, 2006/0108201, 2006/0108202, and 2006/0108203 show various methods of coupling a scraper blade to conveyor belt cleaner, and are incorporated herein by reference.
It is an object of the present invention to provide scraper blades that last longer in operation than many prior art scraper blades. It is also an object of the present invention to provide scraper blades which accommodate smaller size pulleys and yet provide satisfactory wear life. In applications with smaller pulleys where the mounting distance is approximately ¼ of the diameter or less, the shape of the blade with just a single cleaning angle often becomes unusable. In this application, smaller pulleys are considered pulleys having a diameter of approximately between 1 inch to 16 inches. It is also an object of the present invention to provide methods and processes for automating the design of the profile of scraper blades.